BT121-A-V2 is class 2 module?
For reference: class1: 20dBm, class2: 4dBm and class3: 0dBm.
Absolute maximum for BT121 is 12 dBm. You can use API commands to limit the max power. If the module uses more than 4 and up to 12 then you'll be class 1 device. Additionally, there is a Knowledge Base Article regarding the RF maximum transmit power available under below link:
This means that for BT121-A we can use API commands to set 4 dBm then module will be class 2 device?
I think yes. The class of a Bluetooth device depends on its max configurable RF TX power, and if the max is 4dbm or less, then it can be categorized as a class 2.